Radial-shape wireless dog fence system and method

ABSTRACT

A radial-shaped wireless fence system is provided that contains one or more dogs in a user-defined area without the need for a physical fence or underground wire. The system includes a base unit and at least one collar, and is easy to set up and use. Through improved filtering of consecutive distance measurement values taken between the base unit and the collar, errant measurement values are discounted in terms of their contribution to the current estimate of the dog&#39;s distance from the base unit. These filtering techniques, in combination with improved signal strength and antenna diversity in the communication between the base unit and the collar, improve the accuracy and consistency with which the dog&#39;s distance from the base unit is tracked so that unwanted corrections are not administered to the dog.

This application is entitled to and hereby claims the priority ofco-pending U.S. Provisional application Ser. No. 61/282,727, filed Mar.23, 2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to the field of animal containment and,more particularly, to a system and method for defining a wireless dogfence that surrounds a user-defined area and for using the fence tocontain one or more dogs within the user-defined area.

2. Description of the Related Art

Containing one or more dogs within a prescribed area has been achievedin many different ways, most traditionally through the construction of afenced enclosure that is high enough to prevent the dog from escapingthe enclosure by going over the fence. Since some consider above-groundfencing to be unattractive or otherwise undesirable, “invisible” fenceproducts have been developed that rely on a wire buried underground thatdefines a desired “fence” border for the dog or dogs. The wire transmitsa signal that activates a specially designed collar worn by the dog whenthe dog comes within a certain proximity of the border. The collar, onceactivated, can issue an audible warning and/or an electric shock to thedog to ensure that the dog does not leave the “fenced-in” area. Buriedwire systems are labor intensive to install. Further, since the wire maybe unintentionally cut, or otherwise damaged, such as by digging ortilling during lawn maintenance or the like, such buried wire fencesystems are also labor intensive when attempting to find the location ofthe broken wire or other difficulty.

More recently, wireless fence products have been developed that radiatea low frequency signal to saturate a spherical volume which translatesto a generally circular area on the ground plane. The radius of thecircle is user-definable and, according to one such product manufacturedby PetSafe, generally extends radially from about 5 feet to about 90feet. When the dog, while wearing a specially designed collar, is“inside” the signal saturated area, the collar receives a signal and noaction is taken. When the dog moves outside the signal area, however,the collar delivers a correction signal.

Another wireless system is that marketed by Perimeter Technologies, Inc.which, rather than creating a signal-saturated area, uses a distancemeasuring technology between the collar and a base unit to determine therange of the dog from the base unit. However, interference created byobjects often found within a household environment can cause the collarand base to lose communication with one another, resulting inartificially high range values caused by attenuation or reflection,and/or undesired corrections being delivered to the dog, i.e.,corrections when the animal is within the defined containment radius.

Accordingly, a need exists for an improved wireless fencing system thatis easy for the consumer to set up and use and that overcomes theproblems encountered with prior art systems.

SUMMARY OF THE INVENTION

In view of the foregoing, one object of the present invention is toovercome the difficulties of containing a dog within a wireless fenceboundary without administering unwanted corrections to the animal.

Another object of the present invention is to provide a wireless fencesystem having a dual-antenna base unit and a dual-antenna collar toimprove the ratio of successfully received signal transmissions to lostsignals.

A further object of the present invention is to provide a wireless fencesystem in accordance with the preceding objects in which distance valuesare repeatedly obtained between the base unit and the collar and thenweighted and filtered to discount those distance values likely to beerrant and to track more accurately the range of the dog from the baseunit.

A still further object of the present invention is to provide a wirelessfence system in accordance with the preceding objects in which NANOLOC™chipsets are used in conjunction with a power amplification circuitry toprovide greater signal strength for improved reliability in tracking thedog within the fence boundary.

Yet another object of the present invention is to provide a wirelessfence system in accordance with the preceding objects in which thetracking process of the system includes a normal battery conservationmode and an accelerated mode during which the distance value samplingrate is increased in response to the dog's proximity to the fenceboundary.

It is yet another object of the invention to provide a wireless petcontainment product that is user friendly and robust in operation andwhich effectively tracks the distance between a base unit and the dog toreduce the number of inappropriate corrections administered to the dog.

In accordance with these and other objects, the present invention isdirected to a radial-shape wireless fence system for containing one ormore dogs in a user-defined area without the need for a physical fenceor underground buried wire. As used herein, “radial-shape” refers to agenerally circular area defined by a border that encircles a centerpoint defined by the location of the base unit. The border represents anapproximate area within which the collar will begin to initiate acorrection to the dog. This border area marks the start of a triggerzone which extends outwardly from the border in all directions to adistance at which the collar can no longer receive input from the baseunit. This distance, and hence the “size” of the trigger zone, will varydepending upon the terrain and objects between the dog and the baseunit, but can be as much as about a mile and a half from the base unitin open flat country. The fence radius, which is set by the user, is thedistance between the base unit and the border and defines a roamingarea. As long as the dog remains within the roaming area, signaltransmissions are effectively sent and received between the base unitand the collar to monitor the dog's range from the base unit in realtime, and no corrections are issued to the dog. Under these conditions,the collar may be configured to go to sleep to conserve battery power.In addition, the system may be configured to filter out errant valuesand/or to take no action if communication is suddenly blocked, such asdue to loss of power to the base or collar, or the introduction of aphysical signal-blocking element to the system environment.

Also as used herein, the “fence” is an estimated line that runsconcentrically with the border of the trigger zone. In the absence ofany interference or signal attenuation, the fence would be circular,representing the circumference of a circle defined by the radius. Due toreal-world conditions, however, in which signal interference is causedby various objects within the encircled area, or objects anywhere thatcause multipath effects, the generally circular roaming area may havesegments in which the border or “fence” is closer to the base unit thanat other segments, i.e., segments in which the distance between theborder/fence and the base unit is less than the fence radius.

The system includes a base unit and at least one collar for a dog, withmultiple collars also being supported for additional dogs, which is easyto set up and use. Both the base unit and the collar have two antennaseach, providing diversity to improve the ratio of successfully receivedsignal transmissions to lost signals.

The base unit is mounted inside the user's house or other desired indoorlocation. By following a set-up menu on a display screen and using inputelements on the base unit, the user enters a desired fence radius. Theuser then verifies the desired fence radius by walking outwardly fromthe base unit with the collar, noting when the collar outputs a signalindicating proximity to the trigger zone and placing a flag or othermarker at that location. The user then walks back into the roaming area,moves laterally, and then walks back outwardly until the collar againsignals proximity to the trigger zone at which point the user setsanother flag or marker. This process is continued until the completeborder has been marked with the flags or markers. Using these flags asvisual cues of the location of the “fence”, and with the collar on thedog, the user can then train the dog where the fence border is so thatthe dog can be effectively contained therein.

Once the fence has been set up and the dog trained, the system operatesby continuously obtaining distance values between the base unit and thecollar in order to track the distance of the dog from the base unit on areal time basis. These distance values are weighted and filtered todiscount those distance values likely to be errant due to theirdisparity with previously measured values and previous calculatedestimates of the dog's position. More particularly, through weightingand filtering of a plurality of continuously obtained distancemeasurement values taken between the base unit and the collar, anomalousmeasurement values are discounted in terms of their contribution to thecurrent estimate of the dog's location. These filtering techniques incombination with improved signal strength and antenna diversity in thecommunication between the base unit and the collar improve the accuracywith which the dog's range from the base unit is tracked so thatunwanted corrections are not administered to the dog.

These together with other objects and advantages which will becomesubsequently apparent reside in the details of construction andoperation as more fully hereinafter described and claimed, referencebeing had to the accompanying drawings forming a part hereof, whereinlike numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the components of a radial-shape wireless fence system inaccordance with the present invention.

FIG. 2 illustrates the base unit shown in FIG. 1 as mounted inside ahouse to define a roaming area and the trigger zone.

FIG. 3 illustrates the fence border and outlying trigger zone of thesystem set-up shown in FIG. 2.

FIG. 4 is a flowchart showing the steps taken during the fence settingmode of the system shown in FIG. 1.

FIG. 5A is an isolated view of the assembled collar shown in FIG. 1.

FIG. 5B is an exploded view of the components of the collar shown inFIG. 5A.

FIG. 5C is a photograph of the first strap part of the collar strap asshown in FIGS. 5A and 5B, and the antenna to be inserted into the holein an interior end of the strap part.

FIG. 5D is a photograph of the components shown in FIG. 5C after theantenna has been inserted into the hole in the strap.

FIG. 5E is a photograph of the printed circuit board shown in FIG. 5B,as mounted in the lower housing and with the collar straps connectedthereto.

FIG. 5F is a photograph of the collar components shown in FIG. 5B,without the battery, as the upper housing is brought into alignment withthe lower housing.

FIG. 5G is a photograph of the collar components shown in FIG. 5F, asthe upper housing is brought into engagement with the lower housing toseal the correction unit compartment.

FIG. 5H is a photograph of the collar components shown in FIGS. 5F and5G with the correction unit compartment positioned for sealing in anultrasonic welding machine.

FIG. 6 is a flowchart showing the steps taken during the collar settingmode of the system shown in FIG. 1.

FIG. 7 is a flowchart showing the steps taken during the ranging processof the system shown in FIG. 1.

FIG. 8 is a flowchart showing the steps taken during the systemmonitoring mode of the system shown in FIG. 1.

FIG. 9 is a flowchart showing the steps taken during the trackingprocess of the system shown in FIG. 1.

FIG. 10 is a flowchart showing the steps taken during the correctionprocess of the system shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In describing a preferred embodiment of the invention illustrated in thedrawings, specific terminology will be resorted to for the sake ofclarity. However, the invention is not intended to be limited to thespecific terms so selected, and it is to be understood that eachspecific term includes all technical equivalents which operate in asimilar manner to accomplish a similar purpose.

According to the present invention generally designated by referencenumeral 10, a radial-shape wireless fence system is provided thatincludes a base controller unit 12 and a remote unit, generally embodiedas a collar 14, as shown in FIG. 1. For the purposes of training the dogand to provide visual markers for both the dog and the user thatgenerally correspond with the fence border, a set of flags 16 is alsopreferably provided with the system. The number of flags may bevariable, but it is preferred to have from about 25 to about 100 flags,depending upon the radius of the containment or roaming area 32 to bedefined.

As shown in FIG. 2, the base unit 12 is intended to be positioned withinthe user's home 18, garage, or other environmentally controlled, indoorarea, and is preferably configured to be mounted on a wall. While it ispossible to power the base unit with batteries, it is preferably pluggedinto a properly grounded 120V AC outlet. The base unit has two antennas20, 21 for diversity when communicating with the collar 14, a displayscreen 24 (preferably LCD) and input elements or buttons, generallydesignated by reference numeral 26, for inputting information to set upand control the system. According to a preferred embodiment, the inputelements include up and down arrow keys 28, 29 and an enter button 30.

The base unit communicates with the collar using an integrated circuit(IC) chip contained within the base unit. According to a preferredembodiment, the chipset is a NANOLOC™ TRX 2.4 GHz transceiver chipsetsold by Nanotron Technologies of Berlin, Germany. The NANOLOC™ TRX 2.4GHz transceiver chipset is an IEEE 802.15.4a chirp spread spectrum radiomodule with indoor and outdoor ranging capabilities. Other chipsets thatuse the IEEE 802.15.4a chirping technique for radio frequency distancemeasurement could also be used.

The base unit 12 is configured to enable the user to set up acustom-sized fence radius of from about 40 to about 400 feet. As notedpreviously, the radius establishes the distance to the “fence” 31 whichencloses the inner roaming area 32 and establishes the border at whichthe trigger zone 34 begins. While the trigger zone appears to be anannular area or ring 33 as shown in FIG. 3, the ring 33 actuallyrepresents the fact that there is generally some leeway or cushion inthe exact location of the border 31 as compared to the fence radius setby the user, due to signal interference and attenuation caused byreal-world conditions as already noted. Hence, the point at which acorrection is actually initiated could be within or on either the inneror outer edges of the annular area 33.

As summarized in FIG. 4, during the fence setting mode, the base unit islocated at the center of the desired radial-shaped area to be set up,step 40. The user enters the desired fence radius into the base unit,step 40, following a set-up menu displayed on the display screen andusing the input elements or buttons 26 to select the desired parameters.Once the radius has been entered, the user walks to the border with thecollar to verify that the desired radius has been set by noting wherethe collar reacts indicating proximity to the trigger zone 34 and placesa training flag at that location to define the fence 31, step 42. Theremainder of the border or fence 31 is flagged off by the user asdescribed in step 44. A more complete description of the process bywhich the user enters the fence radius and verifies the location of thefence 31 is set forth in the document entitled “Radial-Shape WirelessDog Fence Instruction Manual” which is attached hereto as Appendix A andis considered part of the instant disclosure as if fully set forthherein in its entirety.

As shown in FIGS. 5A and 5B, the collar 14 includes a strap generallydesignated by reference numeral 50 that is fitted around the dog's neckand a correction unit 52 mounted to the strap 50. The strap 50 includesa first part 49 having holes therein that is coupled to one side of thecorrection unit 52, and a second part 51 connected to the other side ofthe correction unit 52 which has a buckle assembly 53 that can beengaged with the holes to secure the collar 14 around the dog's neck.

The correction unit 52 includes a compartment 29 having a lower housing66 and an upper housing 54 with a cover 55 through which a CR123Abattery 56, for example, may be inserted into the compartment 29 forproviding power to the unit 52. The correction unit further preferablyincludes an indicator light 58, preferably an LED post 59 joined to theupper housing 54 with a waterproof adhesive, that is visible from theouter side of the correction unit and, like the base unit, the collarhas two antennas 60, 61 to provide diversity when communicating with thebase unit.

As shown in FIGS. 5C and 5D, the antenna 61 is preferably insertedthrough an opening 46 and into a blind channel 47 in the collar strappart 49 prior to final assembly of the collar and is secured withsilicone or similar material at the strap antenna insertion points.Insertion of antenna 60 into a corresponding hole and channel in strappart 51 is accomplished in like manner.

Housed within the compartment 29 of the collar correction unit 52 is aprinted circuit board (PCB) assembly 65 as shown in FIGS. 5B and 5E-5G.A NANOLOC™ TRX 2.4 GHz transceiver chipset like that in the basecontroller is integrated with the PCB assembly 65 under RF shield 39(see FIG. 5E). The collar and base unit NANOLOC™ chipsets send andreceive radio transmissions from one another like 2-way radios. TheNANOLOC™ chipsets are preferably enhanced in operation with poweramplification circuitry to provide greater signal strength. When radiosignals are sent from the antennas of either the base unit or the collarto the other of the two components, these signals propagate in anomni-directional or spherical manner. Using these signals, the enhancedNANOLOC™ chipsets perform a ranging process with their associatedantenna pairs which continuously captures, filters and refines the datato yield the distance between the base unit and the collar at any giventime, as will be described further hereinafter.

Two probes 64 extend laterally from the lower housing 66 of thecompartment 29 that is against the dog's neck and are insulated from thehousing 66 by electrode grommets 63. Shorter probes 67 can beinterchangeably mounted to the lower housing 66 to better suitshort-haired dogs. Depending upon the setting of the collar, the probes64, 67 provide a physical correction signal to the dog upon reaching thetrigger zone. Alternatively, the collar can be set to provide only anauditory correction signal to the dog. The physical correction signal ispreferably adjustable between a plurality of levels to suit the size,age and temperament of the dog. In a preferred embodiment, the collardefaults to a tone-only correction signal.

To assemble the collar, the ends of the antennas 60, 61 that extend outof the channels 47 are coupled to connectors on the PCB assembly 65,preferably with a snap-on or push-on fit. The PCB assembly is receivedwithin the lower housing 66 with the collar strap parts 49, 51 on eitherside of the lower housing as shown in FIG. 5E. The upper housing 54 isthen brought into alignment with the lower housing as shown in FIG. 5F,and then brought closer to engage with the lower housing as shown inFIG. 5G. Once the upper and lower housing are engaged with one anotherto ultimately close the compartment 29, the correction unit 52 issealed, preferably using an ultrasonic welding machine 81 as shown inFIG. 5H. Once fully assembled and welded as shown in FIG. 5A, the collarand correction unit 52 are sufficiently waterproof so as to be able tobe submerged for a period of about one minute and thereafter operate ator above 75% of accepted specifications for collar performance.

The collar 14 is set up for use with the fence system of the presentinvention using the base unit 12 as summarized in FIG. 6. The consumercan use the base unit to add, delete or change settings for the collar,step 70. To add another collar for another dog, step 72, the userpresses one of the input buttons 26 on the base unit to place the baseunit into a seek mode. When powered on, the collar is programmed tolisten for and respond to a signal from an appropriate enabled devicesuch as the base unit. Upon receiving the collar's response signal, thebase unit identifies the unique media access control (MAC) addressassociated with the collar and stores its identity. Collar correctionlevels and the on/off status of the collar can also be changed using thebase unit, step 74. In addition, collars can be deleted using the baseunit, step 76. A more detailed description of the process by which theuser sets up, activates and deletes one or more collars is set forth inAppendix A, previously referenced and attached hereto.

Once the collar has been set up and activated, the NANOLOC™ chipsetsperform their ranging function to determine the distance between thebase unit and the collar at any given time. The ranging process is asdescribed in connection with the NANOLOC™ chipset on the NANOLOC™website, and is summarized in FIG. 7. Ranging occurs on an ongoing basisunless the collar is asleep. The collar sleeps on lack of motion andwakes up when motion is detected by a motion sensor, such as anaccelerometer, integrated with the collar.

In brief, the first antenna at the base unit determines a first distancevalue between itself and the first antenna on the collar, and thendetermines a second distance value between itself and the second antennaon the collar. The second antenna at the base unit then determines athird distance value between itself and the first antenna on the collar,and then determines a fourth distance value between itself and thesecond antenna on the collar. If all four distance values aresuccessfully determined, the actual distance value used in terms ofobtaining the current estimate of the dog's location is the shortest ofthe four measured values. This ranging process is more fully describedin co-pending application Ser. No. 12/539,404, published as U.S. Publ.No. US 2010/0033339 on Feb. 11, 2010 (“the '339 application”). The '339application is hereby incorporated by reference and considered part ofthe instant disclosure as if fully set forth herein in its entirety.

Having two antennas at each of the base unit and the collar improves theratio of successfully received signal transmissions to lost signals ascompared with single antenna systems. This improved ratio isparticularly helpful in a household environment in which buildings,shrubs, vehicles and other objects can act to interfere with and/orblock signal transmissions. Blocked signals can result in the unwantedissuance of a correction to the dog, i.e., the dog is corrected eventhough still within the prescribed boundary, or in escapes from theboundary if communication is sufficiently blocked.

The double antenna system also provides for dead zone detection andaccommodation. A dead zone is defined as an area in which signaltransmission may be lost or compromised. If such dead zones are notdetected or otherwise taken into account, this omission can result in anunwanted correction being issued to the dog as the system may concludefrom the lack of signal transmission that the dog is outside theboundary. A fuller discussion of the dead zone feature is set forth inthe '339 application.

As summarized in FIG. 8, once set up, the wireless fence system 10maintains a monitoring mode during which the base unit 12 displaysinformation relating to the status of the battery charge level of thecollar 14, the current distance value between the collar and the base,and whether a breach is detected, step 80. The base unit 12 may beconfigured during set-up to sound an alarm when a breach occurs. Abreach is defined as having occurred when the distance value between thecollar and the base unit is greater than or equal to the radius set upfor the fence border, step 82. When a breach occurs, the system enters acorrection mode as will be described further hereinafter.

To reduce the likelihood of an unwanted correction being administered tothe dog, the system according to the present invention includes atracking process which is summarized in FIG. 9. When performing thetracking process, a valid distance value is stored in flash memory atthe base unit, step 90. However, the base and collar continuallytransmit and receive signals to calculate updated distance values on anon-going basis to track the dog in real time. During this ongoingprocess, particular distance values taken at any given time may beslightly inaccurate with respect to the actual location of the dog,indicating the dog to be in the trigger zone when, in fact, the dog isstill inside the roaming area. These errant values, if taken on facevalue, would result in an unwanted correction being administered to thedog. Hence, the tracking process uses an improved Kalman filteringtechnique with hysteresis to “smooth out” consecutive distance values sothat errant values caused by tolerances and attenuation will be ignored,step 92, and a more accurate tracking distance value obtained, step 100,as will be described more fully hereinafter.

The tracking process includes a normal battery conservation mode and anaccelerated mode for the battery 56 of the collar 14. Whether thebattery conservation mode is appropriate depends upon the differencebetween the distance value and the fence radius, step 93. If thedifference between the distance value and the fence radius is greaterthan a threshold value, the tracking mode remains in the normal batteryconservation mode in which the current range to the collar is checkedevery 500 ms, step 95. If, however, the difference between the distancevalue and the fence radius is less than the threshold value, indicatingthe dog to be nearing the fence or border, the system enters a fastrange mode in which the range is checked every 100 ms, step 97. This useof different sampling rates allows for greater battery conservationthrough less frequent sampling when warranted by the dog's positionwithout sacrificing accurate tracking obtained through acceleratedsampling as the dog approaches the fence 31 and trigger zone 34.

As already described, the tracking process also continually compares thedistance value associated with the collar with the fence radius, step94, and, if the distance value is less than the fence radius, no actionis taken, step 96. If the distance value is greater than the fenceradius, however, a correction sequence is commenced, step 98.

As summarized in FIG. 10, the correction process begins when the baseunit sends a command to the collar to correct, step 110. Upon receipt ofthis command, the collar is activated and issues a correction in theform of a tone and/or physical correction, step 112. The correctioncontinues until a set time-out period has been reached, step 114, oruntil the dog returns approximately 10 feet within the roaming area,step 116. If the time-out period has been reached, step 114, thecorrection stops, step 118. If the time-out period has not been reached,step 114, and the dog has returned within the roaming area, step 118,the correction also stops. If, however, the time-out period has not beenreached and the dog has not returned, step 116, the correctioncontinues, step 112. The length of the time out period can be varied,but according to one preferred embodiment the time out period is about30 seconds. The extent to which the dog must return within the roamingarea before the correction is stopped could also be more or less than 10feet according to system design and settings.

To perform the “smoothing out” of consecutive distance values to avoidinadvertent correction of the dog, various types of filtering algorithmsmay be employed to filter the distance values. In a preferredembodiment, the system according to the present invention uses anenhanced Kalman filtering technique as described in Appendix B, attachedhereto and considered part of the instant disclosure as if fully setforth herein in its entirety. Appendix B is an excerpt of a paperentitled, “An Introduction to the Kalman Filter” by Greg Welch and GaryBishop in the Department of Computer Science at the University of NorthCarolina at Chapel Hill.

As a means of further smoothing out consecutive distance values and ofdetecting and ignoring anomalous values, the Kalman filtering algorithmused according to the present invention assigns a weight to eachmeasured distance value according to the apparent reliability orconfidence of the measurement sample. The confidence of the measurementsample is determined on the basis of a comparison made between thecurrently measured distance value and the previously estimated distancevalue as determined by the Kalman filtering algorithm. If the differencebetween the currently measured distance value and the previouslyestimated distance value is greater than a predetermined threshold, thenthe currently measured distance value is considered to be suspect, i.e.,to have limited confidence, and is given little weight. This situationmay be illustrated by the following example. The previously estimateddistance value between the dog and the base unit was 10 feet and thecurrently measured distance value, taken a second later, indicates thedog to be 30 feet away from the base unit. The currently measureddistance value would appear to be errant since, clearly, the dog couldnot have covered that much distance in the time that elapsed. Acurrently measured distance value that represents a realistic movementchange, i.e., that shows a position change less than the threshold, isgiven greater weight when used to calculate an updated estimateddistance value from the base unit to the dog. A more detaileddescription of the weighting process used by the Kalman filteringalgorithm according to the present invention is set forth in Appendix Band is also described in the '339 application.

The confidence of the measurement sample may also be evaluated usingboth a comparison between the currently measured distance value and thepreviously estimated distance value, and an output of an accelerometeron the collar. If the delta between the currently measured distancevalue and the previously estimated distance value is large and “high”acceleration is also reported, then the value is given greater weight,i.e., is considered more reliable. If, on the other hand, a large rangedelta is accompanied by little or no acceleration, then the value isgiven little weight or ignored as likely representing a bad range value.

It should be noted that the converse of the above identifiedrelationship does not necessarily hold true. For example, a low delta inrange values does not become more or less reliable when accompanied bylow acceleration reporting due to the incidence of tangential motionunder high acceleration. But including the input of the accelerometermay be beneficial when evaluating motion radiating toward or away fromthe base unit.

The present invention further achieves enhanced robustness in adverseconditions through strength enhancement of the signals being exchangedbetween the collar and the base unit. This strength enhancement, orsignal amplification, allows the base unit and collar to conduct theranging and tracking processes more accurately than is possible withjust the conventionally configured NANOLOC™ chipsets when operating in ahousehold environment where buildings, shrubs, vehicles, etc., caninterfere with signal receipt and transmission. According to a preferredembodiment, power amplification circuitry is integrated to work with theNANOLOC™ chipsets to provide greater signal strength.

The present invention may also be adapted to track the location ofchildren, as well as other types of animals, through appropriatemodification of the remote unit. For example, rather than a collar, achild could wear a wrist bracelet as the remote unit. The wrist braceletis configured with a NANOLOC™ chipset like that in the collar alreadydescribed herein. The wrist bracelet would not have a correctioncapability, however, but would provide continuous location informationto the base unit, including the boundary breach alert signal, for use bythe parent or other supervising adult as may be appropriate. Similarly,a harness or collar arrangement could be configured for other animalsthat, by providing distance information to the base station, would allowthe owner to track the animal's location, with or without a correctioncapability as appropriate.

The foregoing descriptions and drawings should be considered asillustrative only of the principles of the invention. The invention maybe configured in a variety of ways and is not limited by the dimensionsof the preferred embodiment. Numerous applications of the presentinvention will readily occur to those skilled in the art. Therefore, itis not desired to limit the invention to the specific examples disclosedor the exact construction and operation shown and described. Rather, allsuitable modifications and equivalents may be resorted to, fallingwithin the scope of the invention.

1. A wireless fence system for containing one or more dogs in agenerally circular user-defined roaming area comprising: a base unitincluding a transceiver unit, a location of said base unit defining acenter point of said generally circular user-defined roaming area with aradius of said user-defined area being defined by a user during systemset-up, an area outside said roaming area constituting a trigger zone;at least one collar worn by a dog, said collar including a transceiverunit in signal communication with said base unit transceiver unit, saidsystem configured to continuously obtain distance values between thebase unit and the collar on a real time basis using said transceiverunits and to calculate a current estimate of a distance between the dogand the base unit on an ongoing basis; said collar including acorrection unit that initiates administration of a correction to the dogwhen the current estimate calculated by the system indicates the dog isin the trigger zone; said system being further configured to weight andfilter a plurality of said continuously obtained distance values whencalculating the current estimate and to assign less weight to distancevalues considered suspect due to disparity between said suspect distancevalues and previously measured distance values and previously calculatedestimates of the distance between the dog and the base unit.
 2. Thewireless fence system as set forth in claim 1, wherein said base unitincludes a first base antenna and a second base antenna and said collarincludes a first collar antenna and a second collar antenna.
 3. Thewireless fence system as set forth in claim 2, wherein said system isconfigured to calculate said current estimate by obtaining a firstdistance value between the first base unit antenna and the first collarantenna, a second distance value between the first base unit antenna andthe second collar antenna, a third distance value between the secondbase unit antenna and the first collar antenna, and a fourth distancevalue between the second base unit antenna and the second collarantenna, by comparing said first, second and third and fourth distancevalues to determine a shortest distance value, and then selecting saidshortest distance value as the distance value to be used for calculatingthe current estimate of the distance between the dog and the base unit.4. The wireless fence system as set forth in claim 1, wherein said baseunit and collar transceivers include IEEE 802.15.4a chirp spreadspectrum radio modules.
 5. The wireless fence system as set forth inclaim 1, wherein said base unit and collar transceivers include poweramplification circuitry to provide greater signal strength.
 6. Thewireless fence system as set forth in claim 1, wherein said collarincludes a motion sensor to detect movement of the dog, said collarbeing configured to sleep when movement is not detected for a thresholdtime period.
 7. The wireless fence system as set forth in claim 1,wherein said system is configured to include a normal batteryconservation mode and an accelerated mode in which distance valuesbetween the base unit and the collar are measured more frequently thanin said battery conservation mode, said system being configured to entersaid accelerated mode when a difference between the area radius and thecurrent estimate of the distance between the dog and the base unit isless than a threshold value.
 8. The wireless fence system as set forthin claim 1, wherein said system is configured to smooth out consecutivedistance values using a Kalman filtering technique with hysteresis sothat errant distance values caused by system tolerances and/orattenuation are ignored so as to avoid administration of an unwantedcorrection to the dog.
 9. The wireless fence system as set forth inclaim 8, wherein said Kalman filtering technique includes an algorithmthat assigns a weight to each measured distance value based on acomparison made between the currently measured distance value and thepreviously estimated distance value, said algorithm giving less weightto the currently measured distance value if a difference between thecurrently measured distance value and the previously estimated distancevalue is greater than a predetermined threshold, and said algorithmgiving a greater weight to the currently measured distance value if thedifference between the currently measured distance value and thepreviously estimated distance value is less than the predeterminedthreshold, said distance values when so weighted being used to calculatean updated current estimate of the distance between the dog and the baseunit.
 10. The wireless fence system as set forth in claim 9, whereinsaid collar includes an accelerometer to detect movement of the dog,said Kalman filtering technique further using an output of saidaccelerometer to weight the currently measured distance value, saidcurrently measured distance value being assigned a greater weight if adifference between the currently measured distance value and thepreviously estimated distance value is large and high acceleration isreported, said currently measured distance value being assigned a lesserweight or being ignored if the difference between the currently measureddistance value and the previously estimated distance value is large andlittle or no acceleration is reported.
 11. The wireless fence system asset forth in claim 1, further comprising a plurality of flags placedalong or close to the radius of the roaming area by the user duringsystem set-up, said flags visually indicating a proximity of saidtrigger zone.
 12. The wireless fence system as set forth in claim 2,wherein said collar correction unit includes a compartment containing aprinted circuit board (PCB) assembly, said collar transceiver beingintegrated within said PCB assembly.
 13. The wireless fence system asset forth in claim 12, wherein said collar further includes a firststrap part connected to one side of said compartment and a second strappart connected to an opposite side of said compartment, said strap partsbeing configured to fasten said collar around a dog's neck, said firstcollar antenna being inserted into a blind channel in said first strappart and said second collar antenna being inserted into a blind channelin said second strap part, free ends of said first and second collarantennas protruding from said strap parts being received within saidcompartment and coupled to connectors on said PCB assembly.
 14. Thewireless fence system as set forth in claim 13, wherein said compartmentincludes an upper housing and a lower housing, said PCB assembly and thefree ends of said strap parts being received within said lower housing,and said upper housing being sealed to said lower housing so that saidcollar is waterproof.
 15. A method of tracking a distance between amovable remote unit and a fixed base unit configured as a wireless fencesystem, said system including a base unit having a transceiver unit, andat least one movable remote unit having a transceiver unit, said methodcomprising the steps of: placing the base unit at a location thatdefines a center point of a generally circular user-defined roamingarea; defining a radius of said user-defined area, an area outside saidradius constituting a trigger zone that encircles the roaming area;activating said base unit and said remote unit to bring said base unitand remote unit into two-way communication with one another;continuously obtaining distance values between the base unit and theremote unit on a real time basis to calculate a current estimate of adistance between the remote unit and the base unit on an ongoing basis;and weighting and filtering a plurality of said continuously obtaineddistance values when calculating the current estimate and assigning lessweight to distance values considered suspect due to disparity betweensaid suspect distance values and previously measured distance values andpreviously calculated estimates of the distance between the remote unitand the base unit.
 16. The method as set forth in claim 15, wherein saidbase unit has a first base unit antenna and a second base unit antenna,and said remote unit has a first remote unit antenna and a second remoteunit antenna, said method further comprising the steps of: obtaining afirst distance value between the first base unit antenna and the firstremote unit antenna; obtaining a second distance value between the firstbase unit antenna and the second remote unit antenna; obtaining a thirddistance value between the second base unit antenna and the first remoteunit antenna; obtaining a fourth distance value between the second baseunit antenna and the second remote unit antenna; comparing said first,second, third and fourth distance values to determine a shortestdistance value; and selecting said shortest distance value as thedistance value to be used for calculating the current estimate of thedistance between the remote unit and the base unit.
 17. The method asset forth in claim 15, wherein said step of continuously obtainingdistance values between the base unit and the remote unit on a real timebasis includes the steps of: comparing a difference between the radiusand the current estimate of the distance between the remote unit and thebase unit to a threshold value; operating in a normal batteryconservation mode when said difference is greater than said thresholdvalue; and operating in an accelerated mode when said difference is lessthan said threshold value, distance values between the base unit and theremote unit being measured more frequently in said accelerated mode thanin said battery conservation mode.
 18. The method as set forth in claim17, wherein said distance values are measured about every 500 ms in thenormal battery conservation mode and about every 100 ms in theaccelerated mode.
 19. The method as set forth in claim 15, furthercomprising the step of smoothing out consecutive distance values using aKalman filtering technique with hysteresis so that errant distancevalues caused by system tolerances and/or attenuation are ignored. 20.The method as set forth in claim 19, wherein operation of said Kalmanfiltering technique to smooth out consecutive distance values includesthe steps of: assigning a weight to each measured distance value basedon a comparison made between the currently measured distance value andthe previously estimated distance value using an algorithm, saidalgorithm giving less weight to the currently measured distance value ifa difference between the currently measured distance value and thepreviously estimated distance value is greater than a predeterminedthreshold, and said algorithm giving a greater weight to the currentlymeasured distance value if the difference between the currently measureddistance value and the previously estimated distance value is less thanthe predetermined threshold; and using said weighted distance values tocalculate an updated current estimate of the distance between the remoteunit and the base unit.
 21. The method as set forth in claim 20, furthercomprising the step of sounding an alarm at the base unit when thecurrent estimate calculated by the system indicates the remote unit isin the trigger zone.
 22. The method as set forth in claim 20, whereinoperation of said Kalman filtering technique further includes the stepsof: receiving an output from an accelerometer on the remote unit;assigning a first weight to the currently measured distance value if adifference between the currently measured distance value and thepreviously estimated distance value is large and high acceleration isreported by said accelerometer output; and assigning a lesser weight tosaid currently measured distance value if the difference between thecurrently measured distance value and the previously estimated distancevalue is large and little or no acceleration is reported by saidaccelerometer output.
 23. The method as set forth in claim 15, furthercomprising the steps of placing a plurality of flags along or close tothe radius of the roaming area by the user during system set-up, saidflags visually indicating a proximity of said trigger zone.
 24. Themethod as set forth in claim 15, wherein said system is a wireless fenceproduct for containing one or more dogs in a generally circularuser-defined roaming area, said remote unit including a collar worn by adog, said collar including a collar correction unit, said method furthercomprising the step of said collar correction unit initiatingadministration of a correction to the dog when the current estimatecalculated by the system indicates the dog is in the trigger zone. 25.The method as set forth in claim 24, further comprising the steps of:comparing the estimated distance between the collar and the base unit tothe radius; taking no action if the estimated distance value is lessthan the radius; and initiating a correction sequence if the estimateddistance value is greater than the radius.
 26. The method as set forthin claim 25, wherein said correction sequence includes the steps of:said base unit sending a command to correct to said collar; said collaractivating in response to said command to issue a correction to the dog;continuing the correction until a time-out period has been reached oruntil the estimated distance value is less than the radius by athreshold distance, whichever occurs first.
 27. The method as set forthin claim 26, further comprising the step of activating a second collarto bring said base unit and said second collar into two-waycommunication with one another, said base unit and the collar that wasinitially activated also being in two-way communication with one anotherat the same time.